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Firefox 18 arrives with IonMonkey-powered JavaScript

Mozilla says the newly released Firefox 18 will be delivering faster JavaScript for web games and other long lived applications. This boost is thanks to the addition of the IonMonkey just-in-time compiler as a replacement for the SpiderMonkey JavaScript engine. To get a feel for the performance improvements, Mozilla suggests users check out BananaBread, a WebGL, HTML5 and JavaScript based first person shooter.

IonMonkey was introduced with the alpha of Firefox 18 in September and is designed to improve the performance of long running JavaScript applications; short-running applications will still be run using the JägerMonkey engine. When IonMonkey was introduced, Mozilla's David Anderson noted improved performance over past Firefox and Chrome releases on a number of benchmarks.

Firefox 18 has more than just an improved JavaScript engine, though. The release notes point out that it supports Apple's Retina Displays on Mac OS X 10.7 and later, and it includes initial support for WebRTC, the audio and video real time communications protocol which enables a range of new web applications with real time chat.

Changes from the previous version include better image quality as the developers have changed the algorithm used when scaling HTML imagery, and switching between tabs should be somewhat faster thanks to some performance tweaks. Developers will find that CSS3's Flexible Boxes have now been implemented to allow for a simpler, more responsive style of layout of page elements; window.devicePixelRatio will now give the ratio between physical pixels and device independent pixels on a display.

The CSS @supports is now available to conditionally apply code when a feature is (or isn't) supported, but this feature needs to be turned on by setting layout.css.supports-rule.enabled to true. There are also improved startup times and support of the W3C Touch events is now implemented, in place of the MozTouch events.

Fixes in the release include the disabling of insecure content loading on HTTPS pages, a bug that has been in the Mozilla bug system since 2000. For now though, the fix requires enabling through a setting in about:config. There is also, according to the notes, better responsiveness for users working through proxies. Problems still present from the beta release include Firefox crashing if starting with a locked profile, slow scrolling on Gmail, issues with Microsoft's System Restore and a problem with reporting with the -private flag.